From Friends in Peace and War: The Russian Navy's Landmark Voyage.
At the beginning of the Civil War, the only armed government vessel available to protect San Francisco was the revenue cutter W.L. Marcy, under command of Captain William Cooke Pease. It was a 94-foot topsail schooner that arrived in San Francisco in 1857.
In April 1861, after Fort Sumter was fired upon, the Secretary of the Treasury (the revenue cutters were a part of the Dept. of the Treasury) Salmon P. Chase ordered the Marcy to be fit for sea "for the purpose of overhauling vessels supposed to be contraband of war, or owned by members of the Confederate states."
The Marcy then sailed up the Bay of Martinez to Mare Island for extensive repairs and new armament.
It was noted that this extensive overhaul cost more than the ship had originally cost to build.